Is it a set trigger or plain? Is it dropping into the half cock?
Chances are someone gave the gun a trigger job. They messed with the sear notch and removed metal so it takes less trigger movement to release the hammer but the half cock is still standard height. Normally when the sear is pulled enough to release the hammer it shouldn’t need to pulled more to clear or at least ride over the half cock. The outside edge of the half cock does have a ramp to help the sear ride over it.
Sometimes it works when you pull the trigger more aggressively.
A hammer and possibly a sear. it all depends on what was done to it. The great thing about a 73 trigger is you can remove it from the receiver and work on it and see it function. The first step is get it out and watch it as you slowly operate it by hand and verify if this is the problem.
I got thinking that this also could happen from wear if you no longer have sharp edges to the sear and sear notch since the hammer would release early.
It,s fixed,i replaced the sear,it was a pain in the ass i thought it didn’t matter which way the pin went back, but it does apparently.
Is it possible that a loose trigger bar spring would cause this problem,it was loose and there wasn’t much tension.so i have know way of knowing what the actual fix was.
The pin should be a straight pin unless its worn bad and should go in either direction. Loose or weak spring along with worn pins may cause problems but hard to tell without looking at it.